text:
What effect does tropopause entry have on the FMGC (Flight Management Guidance Computers)?
In my company it’s a procedure to enter the highest tropopause level into the INIT A page. Could someone please explain the effect it has.

It adjusts the FMGC temperature model to account for non-standard temperature. This will have the effect of improving performance predictions by having a more accurate temperature model.
The FMGC uses a temperature model based on the International Standard Atmosphere (ISA). The ISA is based on a sea-level temperature of 15 deg C. In the model, temperature decreases with altitude at a rate of 1.98 deg C/1000 feet up to the tropopause. Above the Tropopause, the temperature is a constant -56.5 deg C.
Updating the tropopause as well as entering the cruise altitude/temperature will adjust the temperature model closer to actual and thus improve predictions. Not entering either value will result in predictions using the ISA model which will reduce the accuracy of predictions (except in the off chance the actual weather matches the ISA.)

Therefore the best flight level may change too or, seen otherwise, this may allow (or prevent) to request a higher FL to reduce turbulence.


text:
Scared of flying in an Airbus A220
The A220 is exclusively powered by PW1500G geared turbofan engines, which have a history of reliability issues.
Multiple airlines grounded their entire A220 fleet amid engine concerns (A220 Engine Woes Continue as More Operators Forced to Ground Airframes – Airways)
In September 2023, P&W recalled almost all of its 3,000 geared turbofan engines. (Pratt & Whitney Parent Stock Punished as Airbus Engine Defects Force Large Recall - The Messenger)
Also in September, the FAA issued an Airworthiness Directive for the engines. As did Transport Canada, stating that "high altitude climbs at higher thrust settings for engines with certain thrust ratings" may be a contributor to the failures, and cautions that "this condition, if not corrected, could lead to an uncontained failure of the engine and damage to the aeroplane".
This whole thing seems like a disaster and I’m terrified of putting my life in the hands of a PW1500G engine (flown by JetBlue on Friday). Is there any reason why I shouldn’t be? :)

How will you be getting to the airport?  Flying in an airliner with a relatively poor safety record is still orders of magnitude safer than travelling by car, for example.

Driving in a car

You have confidence in the FAA when they issued an A.D. concerning the engines. Then later, you do not have confidence in the same FAA when they accept that the engine is safe for flight.
Seems hypocritical, doesn't it?

Did they recertify it? I missed that

@Jim I don't know if they did or not. Its pointless to your question. The point is the FAA has approved it for flight (in some form-or-fashion). Why isn't the FAA's approval enough for you? You seem satisfied with their Airworthiness Directives, but not their approvals?

To add anothe point to the other answers and comments: as any other jetliner, the A220 has been designed and certified to safely takeoff, fly and land even with one engine only. So even if one engine becomes inoperative, there's not a real safety issue, like all the other flights which had a problem with the engine demonstrated.

FAA has issued the AD so the problem can be corrected. Unlike 737 Max at the time was grounded.

If you actually monitored the actual stream of ADs issued all the time on different airplanes, you'd probably quit flying. There is a complex risk assessment and mitigation process followed. I used to participate in this sort of thing.

If the ideas of "employee of FAA are corrupts and therefore they may do a good job in checking issues to get bribed to solve them" is lingering in your brain, please remember that all intelligent people shows a minimum of empathy. If they do not have empathy, or they are not intelligent, they end up being succesful CEOs of random companies or dead in some criminal gang business ... surely not FAA employees ;)

If the A220 and PW1500G are 'too scary' for you, what aircraft and engine would be acceptable?

Jim, I have to ask you this: what is your chain of thought that gets you from "Catching faults in time before they do harm" to "I am going to get harmed"? How does the latter follow from the former? What is your logic there?

The JetBlue plane I’m flying on today is 1 month old.

@Frog That's not necessarily true: https://travel.stackexchange.com/questions/184329/is-there-list-of-the-least-to-most-dangerous-transport-types-sorted-not-by-jour

Your evaluation is not based on logic or rationale, so there is no way your concerns can be addressed with such. Engine failures that result in injury are very rare with passenger airlines. https://www.airsafe.com/events/models/rate_mod.htm

Multiple airlines grounded their entire A220 fleet amid engine concerns

Paradoxically, this should make you feel safer, not less safe. The A220 has had zero accidents. Grounding it is not a sign that the airframe is very unsafe, but a sign that the industry takes safety very seriously and is willing to ground fleets for relatively minor safety issues.
The airworthiness directives you quote are several years old. There were minor issues with the A220, which have been addressed and fixed.
Can you say the same about any minor issues that your car may have developed? Have you inspected every hinge and every bearing on a strict schedule to make sure that problems are caught before they ever happen?
To put things in perspective, the most dangerous airplane you could have booked a flight on in recent memory was the 737 MAX before it was grounded following two major accidents. In that time, it flew about half a million flights, so the accident rate was 4 per million flights. The average flight for this plane is a little over 1000 miles, so on average you could have flown on this most dangerous of planes for 250 million miles before being in an accident.
By comparison, Americans drive about 11 billion miles a day, with an average of around 120 fatal crashes every day. In other words, you can drive less than 100 million miles without being involved in a fatal accident.
So the most dangerous plane, a plane that was so dangerous that it wasn't allowed to fly for two years, was still 2.5 times safer than driving. The A220 is much, much safer than the 737 MAX was.

I agree with your answer, but most (all?) of the road crashes are due to negligent behavior of the driver, not because of some technical issues in a properly mantained car.
(Yes, I know, autopilot of the famous car ... wasn't the manufacturer stating in the instructions book that you had to mantain awareness on your car behavior? let's differentiate between marketing comunications and engineering for the sake of this statistics, although they both belong to the technical aspects of ... selling a product)

"The airworthiness directives you quote are several years old. There were minor issues with the A220, which have been addressed and fixed." Unfortunately, this is not correct. The GTF issues are ongoing and, as the article in the OP from just a few months ago mentions, over 1,000 aircraft will be taken out of service for a while over the next few years for engine inspections related to these issues. Personally, I have absolutely zero qualms about flying on a GTF-powered aircraft, but it's not accurate to say that the issues have been resolved.

@EarlGrey Very true. But whether it's a technical issue or a negligent driver doesn't help me if a negligent driver crashes into me. It's plausible that a competent defensive driver in a well-maintained car is safer than a passenger of a pre-grounding 737 MAX. It's less plausible that any driver is safer than a passenger in another airliner that is some 100 times safer.

@reirab The ADs referred to are years old, and what I mean when I say they have been resolved. The first article seems to be referring more to supply chain/maintenance issues, where planes are having to be grounded for long turn-around times. The second article I grant is not about issues that have been resolved- but any plane that doesn't have the required inspections is grounded so I don't see how it's a safety issue.

Why does people say Airframe instead of airplane. Is it just to sound smart?

@Scorb  Airliner engines can and do get replace periodically, so their failure rate / lifespan is different to that of the fuselage. Therefore it is sometimes important to refer to the airframe rather than the 'plane. And sometimes its just a word choice...

How will you be getting to the airport? Flying in an airliner with a relatively poor safety record is still orders of magnitude safer than traveling by car, for example. –
Frog

Driving in a car –
Jimemphasis added

Exactly Frog's point!
Even with the relatively poor record of the PW1500, it's still going to be orders of magnitude safer than your journey from home to the airport by car. (Or by car from the destination airport to final destination.)
Since you're willing to put your life in the hands of other drivers of unknown training and ability and levels of distraction cough cell phones cough, driving vehicles with totally unknown maintenance history to get to the airport, you probably shouldn't be worried about putting your life in the hands of well trained pilots flying a well maintained aircraft even though the engines have a known issue that is in the process of being corrected.
While I don't know the deadline for meeting the ADs on this engine, at least some of them have probably had the appropriate actions taken, meaning that your chances of flying in an aircraft with a problem are lower than they were prior to the issuance of the ADs.
Knowing that the issue exists and knowing likely causes of the issue will help the pilots avoid the situations that could exacerbate the issue. Remember, they all want to arrive alive, too.
Of course, you could always cancel the flight and drive all the way to your destination. You seem happy with those risks...
TL;DR: There is every reason you should not be afraid of flying on Friday, but there's probably roughly zero we can say to convince you of it. That's kinda how irrational fears work.

Re: helping people get over fears of the safety of flying: The youtube comments sections of videos from pilots like 74gear and MentourPilot are full of people saying that learning more about aviation helped them get over their fears.  (Usually that wasn't a specific concern about a specific engine, but I'm guessing the OP has some general fear of flying).  Seeing how much has to go wrong for something bad to actually happen is reassuring, and the fact that when an incident happens, procedures and hardware change to make it less likely to happen again.

Also, incidents where pilots were able to save a damaged plane should instill confidence: even an uncontained engine failure (of one of two engines on the plane) is going to make the flight exciting (tiny chance) but probably most of the passengers and crew will still survive.  Planes are pretty robust; a lot can fail and still be landable.  (Uncontained engine failure sending fan or prop blades into the cabin is super bad, though.)

Fair points, @PeterCordes, however fear of flying (among other phobias) are generally irrational (as all the rational arguments point out), and no amount of rational though will help some people. Yes, some can be helped, but not all...

A lot of the comments I remember seeing described still having fear, but being able to deal with it through knowledge and stay calm enough.  Things like knowing what procedures were happening with the noises the plane was making during take off and climb, and stuff like that.  Being able to recognize that your fear is irrational is a big help for some people.

Do you have a source for your "orders of magnitude safer" (that is, 100s of times safer) assertion? For starters, the plane trip will presumably be 10s to 100s of times longer than the car trip, so on a mile-for-mile basis the plane would have to be something like 1000 to 10,000 times safer for your assertion to hold up.

Part of the "fear of flying" is also "fear of not being in control"  or "not being the driver"   You're putting trust in someone else's ability to control a vehicle.  Probably this whole post has a parallel question on https://psychology.stackexchange.com/

@SteveBennett The Airbus 220 has had zero losses. Technically that makes it infinitely better. :) Practically, we can calculate the worst-case odds, assuming an A220 will crash the very next minute - and you're still looking way better on the plane.

The JetBlue plane I’m flying on today is 1 month old.

Which gives you every reason to believe that the engines on it are also brand new and do not have the issues you've noted.

If the FAA issued and AD, and the airplane is continuing to fly at this point, that means that the operator is in compliance with the corrective fix listed in the AD.  As to your safety on that flight, you will not find a safer way to travel than on a Part 121 scheduled air carrier flight.
Keep in mind a recall does not necessarily mean a dangerous or defective item is currently in use, provided the operator applies the corrective fix recommended by the manufacturer.  Cars are constantly recalled by manufacturers. Typically all that’s involved is the installation of a repair kit that remedies whatever potential safety issue(s) exists.  Likewise, aircraft manufacturers have service engineering groups, which identify an address potential safety risks in their products before problem occurs.

Good point on the automotive recalls! When a CAA issues an AD, it's mandatory that the item be fixed. When a car manufacturer issues a recall, they might not even be able to notify every affected vehicle's owner, and even if they do, it's entirely optional for the owners to bring the vehicle in to get it fixed. I've looked at used cars to purchase and discovered 3 or 4 outstanding recall issues on them, and these vehicles had been on the road on a daily basis just weeks prior.

The JetBlue plane I’m flying on today is 1 month old.

If the airplane is one month old, it’s probably still gonna have a new car smell. You’ll be fine. Trust me.

One way to view this conundrum is to view the risk/reward profile of the situation.
Is there risk involved? Yes.
Is there more risk involved than most other things you do every day? Probably not.
Is there more reward in going on your trip than staying home? That's up to you to decide.  But unless you literally stay at home and board up the doors and windows, you will likely be exposed to more risks than flying on that aircraft.  And even if you do stay at home and board up the doors and windows, you risk death by being trapped by a fire.  Or carbon monoxide poisoning.  Or food poisoning.  Or electric shock.  Or crushed by a falling ceiling fan.  Or breaking your spine falling down a flight of stairs (which happened to a friend of mine).  You get the idea.
Another question to ask yourself is why you know so much about the specific engines in the aircraft being used for that trip.  Most commercial passengers have no idea what aircraft they will be traveling in, nor have any idea what engines are affixed to those aircraft.  This suggests either you're involved in the aviation industry or you're possibly dealing with a painful anxiety issue.  If it's the former, you know how relatively safe properly maintained commercial jumbo jets are compared to most other modes of transportation.  If it's the latter, I compassionately mention that treatments are likely available.
(I say this with particular compassion because, when I was young, I once freaked out - for no obvious reason at the time - on the way to an airport to board an aircraft.  It was a terrifying experience, so I know the pain firsthand.)

At the moment I'm writing this, there are about 120 Airbus A220 in the air:

There is nothing particular about today. This happens every day, there 100+ A220 in the air pretty much all day long. So 10,000+ persons fly in an A220 each day, every day. And the A220 has been involved in a grand total of zero accidents. Feels pretty safe to me.

What is the reasonable worst case you expect?
If the engine is reputed for having infrequent mechanical failures, you are talking about a single-engine failure. That is a scenario pilots actively train for and procedures are designed for.
For instance, during takeoff there is a callout at a pre-calculated decision point: prior to that, you respond to a single-engine failure by stopping, after it you take off anyway on the single engine, then return to the airport.  This isn't luck and and prayer; it is all designed, calculated and planned ahead. The procedure is a memory item meaning the pilot must prove they know it by heart to keep their type rating, and demonstrate it in full motion simulators. And single engine failure is frequently tested.
They have also trained out many of the common mistakes made in this procedure, such as shutting down the wrong engine or failing to deal with differential thrust.
So you might just lean into your imagined failure scenario and see just how bad it isn't.

This is true for normal engine failures, but you missed the key word "uncontained" (and "damage to the aeroplane").  High-RPM rotating parts have a lot of kinetic energy, but the engine housing is designed to contain that even if a fan blade cracks due to metal fatigue or bird strike or whatever. (Containment is part  of engine certification.)  An uncontained engine failure can involve a fan or turbine blade being thrown out towards the fuselage or wing at high speed, and this AD specifically calls out the possibility of damage to the plane. That's cause for rational concern and digging deeper

e.g. https://www.forbes.com/sites/danielreed/2018/04/17/the-worst-thing-that-can-happen-to-a-jetliner-in-flight-just-did-it-killed-one-southwest-passenger/?sh=44c090131513 is a 2018 story about an uncontained engine failure that killed one passenger on a SouthWest flight.  That article describes it as "The Worst Thing That Can Happen To A Jet In Flight", which is somewhat hyperbolic.  (e.g. elevator or aileron physically stuck at max deflection make a crash inevitable, like the pitch-trim jack-screw in the MD-83 https://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261)

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text:
What makes the MV-22 has lift thrust and its disk loading is so high?

Image source:
The above is comparison table of several rotating wing aircraft's disk loading, especially I highlighted the disk loading of MV-22 Osprey tiltrotor versus CH-47 Chinook helicopter. As in the table, the disk loading of MV-22 = 129.63kg/m2 with 38ft rotor diameter each while disk loading of CH-47 = 43kg/m2 with rotor diameter is 60ft each. Both of them come with 2 rotors and 3 blades each rotor. If we see that table, the disk loading of MV-22 is three times of disk loading of Chinook's with their blades' length is more than double/half one of another. Means, the lifting thrust of the MV-22 is very high. So my question, what makes the MV-22 has lift thrust and its disk loading is so high?

Your question considers both the CH47 and MV22 rotating wing aircraft, but this is only partially true for the MV22 which also operates as a fixed wing aircraft with rotors tilted forward acting as props.
A prop requires a higher velocity through the disc than the aircraft's airspeed or it ceases to produce thrust. The MV22 flies at 240kt so the airflow needs to be higher than 240kt. The CH47's rotors even at speed see very low inflow velocities, so it uses a much lower disc loading to increase lift efficiency.
This shows a rough relationship between disc loading and air velocity through the disc. As disc loading increases hover efficiency drops but downwash speed increases, so the MV22 uses a higher disc loading to get higher airflow speed through the props.

I am asking when it V/STOL as mentioned in the table. Not a case when it cruise. I am asking when it VTOL, what makes it so powerful. The rotor it self is shorter 5ft that it should be, but due to storage necessity, it made just 38ft. Just at 480 RPM the rotor's tip speed will not exceed Mach 0.85. Clearly, it can not rotate faster. Then my question, what special design in that rotor's blade so it has so powerful lift?

CH22? Please make up your mind!

According to your plot, the MV-22's disc loading of 130kg/m² gives an induced velocity of some 100km/h which is definitely well below the MV-22 flying speed of 450km/h (240kts). How is this compatible with your statement that "the airflow needs to be higher than 240kts"?

@PeterKämpf fixed, thanks

@sophit This plot illustrates the principle for the case in the reference, which describes a different aircraft in hover. It is not the MV22. It would have to be adjusted to apply to any other aircraft and particularly in cruise, but the principle still holds.

@AirCraftLover Are you asking how to design a rotor for the MV22?

@Pilothead, as in my title, "What makes the MV-22 has lift thrust and its disk loading is so high?" The blades' diameter their selves are shorter 5ft each than they should be. Their diameter should be 43ft to make them have proper disk loading. But, due to some constraining, they are cut. As we know, we can not just force the rotors to spin as fast as possible due to sonic-boom. In my calculation, with current blades diameter=38 ft, their maximum rotation speed is just 480RPM. Question, how that so short blades can have so hight lift?

@Pilothead, just like an airplane, airplane need wide area wing (https://en.wikipedia.org/wiki/Wing_loading) if it is bigger as there is linear relation between load and wing's area. But a bit different with rotary wing, in rotary wing we calculate the disk area.

@AirCraftLover: what do you mean with "Their diameter should be 43ft to make them have proper disk loading"? What's a proper disc loading value?

@Pilothead: anyway, the MV-22 has actually an induced speed of 80kts. Again, how is this compatible with your statement that "the airflow needs to be higher than 240kts"?

@sophit Obviously, in cruise the MV22 props are not working on static air.

Agreed, then you should modify your text because as it is know it seems to suggest that the induced speed must be higher than 240kts which is not

What makes the MV-22 has its disk loading is so high?

Compromises. As usual in the aerospace world.
In particular, here we have the following two contrasting requirements the equilibrium of which drives the design of a tiltrotor resulting in its relative high disc loading in respect to a pure helicopter:

in helicopter configuration the blade span should be as big a possible to have an efficient design requiring less power to work, but;
in airplane configuration that same blade cannot be too big in order to limit its tip speed under the speed of sound.

Disc loading influences the power $P$ needed by a rotor to generate a certain amount of thrust $T$ according to the following simple equation:
$P=\sqrt{\text{(disc loading)}\frac{T^2}{2 \rho}}$
Being the thrust kept constant, a higher disc loading implies more power which has to be supplied to the rotor to give that thrust. So, in order to keep power required low, disc loading should be also low i.e. disc area as big as possible. For example, at the extremes of the table you posted, on one end there might be a man-powered helicopter with a very big rotor $\Rightarrow$ low disc loading $\Rightarrow$ low needed power; and on the other end an F-35 with its very high disc loading $\Rightarrow$ very high power required.
Anyway the rotor of a tiltrotor cannot be too big since it has to work also as a propeller when the aircraft is in airplane configuration. Propellers also obey to the same previous equation but with an additional limitation: the speed seen by a propeller is the sum of the speed due to its rotation (just like a rotor in hover) plus the flight speed. This sum is highest at the tip of the blade and it must be lower than the speed of sound in order to avoid transonic effects that increase drag and reduce thrust.

Obviously there are many other requirements/constraints which have to be considered in the design of a tiltrotor, like for example:

rotor assembly should be kept slender to reduce weight; this help limiting both CG excursion and aeroelastic effects during transition phase;
blade span is limited by obvious reasons of clearance with the fuselage when in airplane configuration; longer blade would imply a wider wing to keep the blade far from the fuselage giving an higher wing weight;
airflow velocity under/behind the disc rotor (aka induced velocity) is also proportional to disc loading, according to the following equation:
$v_i=\sqrt{\frac{\text{(disc loading)}}{2 \rho}}$ and with its 80kts the induced velocity under the MV-22 can be classified as a hurricane; that means that the MV-22 cannot for sure land on some unprepared field; high induced velocities increase also the risk of brownout/whiteout; and the fuselage is better accessed from behind instead from the side where the high induced velocities can make it difficult.

when you introduce formulas, please introduce also the symbols therein contained.
T is the thrust
{\displaystyle \rho }\rho  is the density of air (or other medium)
A is the area of the rotor disc
P is power

@EarlGrey: done

Unlimited power is not always solution. If the rotor length of the MV-22 is just, i.e., 2m (diameter=4m), even with unlimited power will not be enough to lift that aircraft in maximum load. There is limitation such as sonic boom. I am asking specific MV-22, not general. The rotor of the MV-22 itself is shorter 5ft than it should be. Then my question was, what makes it lifting force so high? There must be specific design.

@AirCraftLover I actually wrote the opposite: the rotor should be big to reduce power but on the MV-22 the rotor cannot be as big as needed since there are other limitations like supersonic speed at its tip and clearance with the fuselage. Sonic boom happen when the entire aircraft flies at supersonic speed, I really don't think that the MV-22 can fly supersonic. Please don't downvote before understanding things.

Another constraint for rotor diameter in the MV-22 is span: Larger rotors require a larger wing, which is heavier.

@PeterKämpf: good point, I'll expand my answer with it

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text:
How does the Sikorsky Defiant X make yaw as it has no-tail rotor?

That picture I took from here. To understand my question I suggest you to watch it just 10s, just very short, but it will show you very closely when that Sikorsky make yaw. As it is no tail rotor like commonly has in every helicopter, it has propeller to push only (called pusher compound rotor), then how does it make yaw? In that video (just simply click it, it will take you the part I want to show), it make yaw when it being hover and the propeller is not even rotating. Hence, it is clear that the propeller is not involved to make yaw.
Then, how does it make yaw?

I am pretty sure that the Yaw-control is used in this Sikorsky Defiant-X is not the same as it does with other coaxial rotor helicopter. If we see very carefully the main rotor by play it only 25% speed on YouTube, we will se that there is no changing with the rotor pitch, either the upper or the lower. I suspect, its Yaw-control is performed using bleed air like it does with VTOL F-35C.

https://www.boeing.com/features/2022/07/defiant-pilots-talk-future-long-range-assault-aircraft.page  Yaw control is managed by the flight controls using differential main rotor torque.

@Jim, as I said, that is probably true for another, but for this Sikorsky Defiant-X, it seems like not really. Have you watch it closely?

@AirCraftLover Jim is right. In the link he provided, the test pilot explicitly states that differential torque is used. The video you linked only has very little yaw rotation, plus it is a sustained yaw rotation, which would require only very little to no input, hence you might not see it. Additionally, a bleed air system like you proposed would be heavier, than just using the existing control. Using differential torque or differential cyclic input to the main rotors is state of the art and established for coaxial (and flettner) rotors.

"… tail rotor like commonly has in every helicopter …" to my knowledge neither all the Kamovs nor many of the Kamans have a tail rotor.

@PeterKämpf, single rotor helicopter I meant, not the coaxial one.

"If we see very carefully the main rotor by play it only 25% speed on YouTube, we will se that there is no changing with the rotor pitch": do you really think to be able to see a half degree pitch variation from a video on YouTube? "its Yaw-control is performed using bleed air": from where and toward where?


text:
Between hover and moving straight forward, which one is this Sikorsky uses more power?

Source:
Consider this Sikorsky–Boeing SB-1 Defiant is being flying forward level and straight and being hover, which state is consumes more power? For both states, we assume that air is very still and calm for both states so we may neglect its effect, nor rain or anything else that makes one weather condition is different than the other. As we know, this helicopter is coaxial rotors and for moving forward it is powered by its tail rotor. Of course, that tail rotor consumes power so its power consumption we exclude from power calculation. What behind my question is for hover, the helicopter stay in one place and the rotors always in a disturbed air while when it is being moving straight forward and level (means no cyclic applied differently), some part of the rotors disk always gain new undisturbed air.

Does this answer your question? Do helicopters use more fuel when hovering?

Not same case as it was not dealing coaxial rotors. For single rotor, there is cyclic application while with coaxial rotors there is not.

"Not same case" they both rely on exactly the same phisics and aerodynamis. "For single rotor, there is cyclic application while with coaxial rotors there is not" if there's no cyclic how is it controlled then?

Where did you learn how to fly single rotor helicopter and that Sikorsky coaxial rotor? Single rotor's moving forward is based on cyclic application while this Sikorsky coaxial rotor its moving forward is pushed by its tail rotor. No cyclic applied when it is moving forward.

And to fly sidewards? Anyway forward thrust is given by a mix between forward cyclic and thrust from propeller.

It is exactly the same case as with a single tilt-rotor, or a coaxial tiltrotor, or a simgle rotor with push-propeller. In all cases, transitional lift causes less required power: the induced power reduces.

This is actually very well researched and is discussed in a lot of papers on this topic, and can be nicely graphed for example in the following figure. Please note, I pulled all of the following graphs from this publication*.

BL is a normal helicopter configuration, CCH stands for Coaxial Compound Helicopter. The paper exercises this on the example of a compounded Lynx helicopter as depcited in the following.

Look at the bottom right of the first graph, you will see the total power required over airspeed. You recognize from this graph, that the power for both configurations is medium high at hover, then drops as the airspeeds gets higher and reaches a minimum at around 75 knots, which is fairly typical. Then the increasing airspeed takes its toll, and you need more and more power to overcome the additional air drag. The only difference between a normal helicopter and a compound helicopter is that the top speed is higher for the compound helicopter as can be seen in that graph.
You specify in your question that you want to exclude the pusher propeller at the back, but the answer stays the same. Middle power levels at hover, low power levels at around 60-80 knots, and after that increasingly more power until you reach the power limit of your engine.
*I am in no form affiliated with the authors or this publication. Its simply the first one I found.

If you exclude the power required for the tail propeller (per your thought experiment), the rotor disc will still require significantly more power to hover than to fly forward.  A coaxial rotor does not reduce the aerodynamic benefit of translational lift,  nor does it solve the ring vortex problem.
Even if the rotor disk is kept horizontal (no cyclic tilt) it will still benefit from translational lift.  The upside to translational lift is not a function of cyclic rotor tilt.  In fact my intuition is telling me that the flatter (more horizontal) the orientation of the rotor, the more it benefits from translational lift.  A cyclic-tilted rotor disk is acting on air that already has downward movement through the disk by virtue of the forward motion of the helicopter in a nose-low attitude.  Think “swimming upstream.”  A horizontal disk is acting on still air that does not already have some downward momentum through the disk.


text:
How to calculate lift/thrust effect of adding blade to a propeller?

Source:
Say I have blades of a propeller of an aircraft (airplane or helicopter). The blades have exactly the same profile, size, dimension, and weight, and will be coupled to a shaft with the same shaft power. I will test the propeller if I have only install two blades. Then I will try 3 blades, then 4 blades (of course there will be engineering work to make them work). My question is, what is the formula to calculate the thrust/lift blades number is in variable (say in n-blades, which by adding more blades will add weight too to the total load).

If the geometry of the blades is kept constant, then thrust and torque is simply proportional to the number of blades $N_b$.

What you need is called Blade Element Momentum Theory (BEMT) and it is something more advanced than the simple momentum theory (where there's no sign of actual blade geometry) but still simple enough to be solvable by hand.
It is based on the hypothesis that any blade is composed by a continuous sequence of adjacent airfoils, each of them generating therefore lift and drag according to the simple and well know $l=½ \rho V²S C_l$ and $d=½ \rho V²S C_d$.
$V$ is the local airflow's speed seen by each slice of blade and is given by the sum of the following 3 terms:

the speed due to the rotation of the blade around the shaft; this speed varies linearly along the bladespan from 0 at the root to $\omega R$ at the tip, where $\omega$ is the rotating speed and $R$ the bladespan;
the speed at which the propeller is flying with the aircraft;
during its rotation, the blade bumps into the wake shed by the previous blade; and after one complete rotation, it bumps into its own wake; these wakes have also to be taken into account.

Terms 1. and 2. are know, since $\omega$, $R$ and the aircraft's speed are known; the speed 3. due to the wake depends itself on the lift and gives rise to a vicious circle: the lift depends on the wake and the wake depends on the lift! This vicious circle is broken by either using simplified models of the wake and/or wind tunnel measurements and/or CFD simulations.
Once lift and drag for each slice of blade have been calculated, they are summed up (integrated) along the bladespan, from root to tip, to get total lift and total drag per blade; these lift and drag are finally decomposed in 1) a force parallel to the propeller shaft, which is the thrust generated by the propeller; and 2) a force perpendicular to it, which gives the torque needed to make the propeller spin.
Let's make a simple example built upon the following simplifications:

the aircraft is at rest, i.e. term 2. is null;
the wake in/upon the propeller is constant everywhere, i.e. term 3. has a constant value;
the blades have a hyperbolic twist, which is a good approximation of real propellers;
and each airfoil is operating at its $\alpha$ of maximum efficiency i.e. maximum $C_l/C_d$; this is also a good approximation for variable-pitch propellers.

Then we get that:
$C_T=¼ \frac{N_b c_{tip}}{\pi R} C_{l_{\alpha}} \alpha_{@maxC_l/C_d}$
where:

$N_b$ is the number of blades;
$c_{tip}$ is the chord at the tip of the blade;
$C_{l_{\alpha}}$ is the slope of the airfoil's lift coefficient;
and $\alpha_{@maxC_l/C_d}$ is the airfoil's $\alpha$ for maximum efficiency.

Also for cases more complicated than the one in this example, BEMT can be used to get $C_T$. For a complete overview I'd suggest you to have a look at some standard books about helicopter aerodynamics: as seen, the theory behind isn't that complicated but for sure is a bit lengthy.
Note that in the propeller (or helicopter) world a coefficient of thrust $C_T$ exist and not of lift! From $C_T$, the thrust is calculated with an equation similar to the one for lift or drag but based on the speed of the blade's tip and the surface of the propeller disk:
$T = ½ \rho (\omega R)^2 (\pi R^2) C_T$
P.s.: if you are interested, I gave a very similar answer but applied to Ingenuity.

It's interesting, but I cannot understand the mathematical integration of the blade elements, and are thus, not able to derive the total thrust...

Let me take some times to learn your priceless comment, I will be back soon. Yes, it look like not as simple as I thought. Thanks

@xxavier: yep, I forgot that part. Now it's updated

@AirCraftLover: I updated a bit the answer and provided with a link to an example about Ingenuity. Hope it helps

How and where did you get your coefficient of thrust (Ct) formula? Do you have reference of it? I spent more a month to digest your formula do you have reference of it? I assume you tried to involved blade solidity ratio to your formula.

@AirCraftLover sure: G. Leishman, helicopter aerodynamics. Have fun with it.

"For a complete overview I'd suggest you to have a look at some standard books about helicopter aerodynamics." What is that Coefficient of thrust exactly? Helicopter, or propeller? As far as I know, propeller is using propeller pitch (in m or inch depend on the standard is used).

@AirCraftLover: The theory and the physics behind is exactly the same between propellers and rotors. Pitch is an angle, so it should be in degrees or radians. The $C_T$ must be used in the thrust equation as given at the end of my answer.

Propeller thrust ratings are (unfortunately) avoided by many people because of a variety of factors that affect prop performance.
Matching props to engines can be done by trial and error, refined by previous experience matching engine horsepower to prop pitch and diameter.
However, prop thrust output is strongly dependent on airspeed.
Let's go from a 2 blade to a 3 blade.  The engine must work harder to achieve the same RPM due to prop drag.  Assuming it can reach the same RPM (this would usually take a larger engine or turbocharging), the new found thrust improvement can be tested as follows:
Try flying Vy and see what your pitch angle is to the horizon.  Assuming no changes in aircraft drag, your 3 blade should be giving a greater angle of climb.
Now you can calculate the thrust improvement by comparing 3 blade sine climb angle × weight and comparing it to the 2 blade sine climb angle × weight.
What will probably be found is that the increase in rate of fuel consumption will be greater than the performance gain because of prop blade interference.  If fuel consumption (horsepower) is held constant, the 2 blade will outperform the 3 blade.
Fuel consumption flying Vy in level flight provides some idea of aircraft drag at that speed (for total thrust estimation), but will be somewhat skewed by prop and engine efficiency issues at lower operating RPM.  Airframe drag can also be calculated from glide ratio as sine angle of descent × aircraft weight.

"The engine must work harder to achieve the same rpm due to prop drag." Of course. The additional blades itself will give more weight, the centrifugal loss affected will be bigger. They will be taken into consideration as our ultimate goal is efficiency, whether it will give benefit.

The only reason to add blades is space consideration.  I would look at the Martian Ingenuity for other ways to improve efficiency while adding blades.

My question is: what to be considered when we add more blades. Once I read, the most ideal aerodynamic is using single blade, but however it will be unbalance. So, how to forecast effect of adding more blade to the propeller, like maximum angular speed (RPM), chord length (C), and blade length (R) ==>> Hence we need to consider about ratio between RPM and the propeller solidity ratio.

@AirCraftLover adding another blade with the same power slows RPM down due to higher drag.  But you can compensate by running at a lower pitch.  Again just like wings, you try for optimal AoA for your prop blade.

Yes, of course. But consider we may keep the angular speed is maintained by adding the Shaft HP (SHP) driving it. Then how to do that calculation? There must be physic formula, at least as tentative reference.

@AirCraftLover but you say in your question "same shaft power", now you want same RPM, which requires more power, therefor more weight (turbocharger may help here).  So, try as we may, there is no simple formula.  Too many variables.  What is outlined in the answer is a practical way to test thrust output by adding blades.  Two major variables are power output of engine and prop efficiency to generate thrust at a given airspeed.


text:
What is the meaning of "Contra-Rotating Propeller Increases Efficiency"? How is it calculated?

This picture is taken from here.
In that video is mentioned that contra-rotating propeller increases efficiency up to 6-16%. Regardless of the number that could be vary from one airplane to another, what I am asking here are: how the efficiency increase is calculated, how it is compared, to what parameter the efficiency increased is compared? Is it representing overall efficiency after calculated including the weight it added? The noise it created we may neglect, not part of my question.

So you are asking if there is a standardized, generally accepted definition of the "efficiency" of a propulsion system, and does this definition take the weight of the system into account?  Or you are asking what the intended meaning of efficiency would most likely be in the particular context of the quote in this video, i.e. what this particular author intended?  Not exactly the same question, could be some room for clarification here.

@quietflyer, Yes, more or less like "does this definition take the weight of the system into account?". Because, when it measured the trust alone it can be increased. But when it is put to the air plane, the additional device to make contra-rotating will give more weight, which in turn need more thrust/power to push the airplane to make it fly. I just don't have a clear understanding whether the efficiency is measured as standalone or as overall when it mounted and used in the airplane.

@quietflyer, say that we have two identical airplane,  one is using single rotating propeller and another one is contrarotating propeller. Both the airplane fly form one place to the another place at the same time. Will the contra-rotating propeller be more efficient to compared the one with not contra-rotating? I hope you understand my question. Sorry for my English limitation to make a good phrase.


text:
Why the pitch control of helicopter is named Collective Control? And why does it located at the left side of the pilot seat?

This is probably a very trivial for some of you. But sometimes a name not representing the function become a question, just like this Collective Control, which its function is to pitch up the blade when it pulled up, and vice versa to pitch down when it pulled down. Why that device is named Collective Control? Why not another name, i.e., Pitch Control, Lever Control, etc., which is seem more representative. And why does it located on the left side of the pilot seat?

To come at it from another perspective - what would you rename them as? Keep in mind: The collective control is used to control the pitch of the rotor blades. The cyclic control is also used to control the pitch of the rotor blades. They are both pitch controls. The collective can control the position as well as the speed of the heli, while the cyclic can control the attitude as well as the position of the heli. What they control depends on the state of the helicopter at a given point in time.

You seem to be using comments below to argue with people who have presented valid, reasonable, and complete answers. Combined with some of your word choices in the question, it seems like you may not be a native English speaker. This begs the question: Are you sure the problem is in the name of the helicopter control and not in your use or understanding of the English language?

"Collective" is short for "Collective Pitch Control", which, you know, controls the pitch of the blades collectively.
It's on the left side because the really fine motor control required of flying a helicopter with the cyclic is best suited to the right hand, and 90% of the population is right handed.
A lot of machines (Hughes and others are exceptions) are flown from the right seat because the collective hand is the "free-est" you might say, since you can let go of collective but are not supposed to let go of cyclic.  Flying from the right allows you to work all the switches in the cockpit without taking your right hand off cyclic.  On left seat solo machines like Hughes 300/500s or Bell 47s or Enstroms, you have to switch hands all the time any time you want to work a cockpit control.

"Collective" is short for "Collective Pitch Control" This is the answer I am looking for.

It's on the left side because the really fine motor control required of flying a helicopter with the cyclic is best suited to the right hand. Thank you for the logic behind the design.

Firstly, it does not control the pitch of the helicopter, that can be achieved using the cyclic control.
Secondly, it is named collective because it changes the pitch of of all the main rotor blades collectively, as in, at the same time and by the same amount.
This is different from the cyclic control which adjusts the pitch of the blades as a function of where they are in their cyclic rotation around the helicopter, i.e. as a function of their azimuth.
As for why is it on the left, that is because the majority of the population is right handed and the cyclic demands more precise and complex inputs. Therefore it is easier for the pilot to have the cyclic stick in their dominant hand.

I have explained the function to control the blade. My question is, why the name not representing its function?

What part of my second paragraph is unclear? It does describe the function!

Both the cyclic and the collective change the pitch angle of the main rotor blades. The cyclic is typically located in front of the pilot and is controlled with the right hand (presumably because most people are right handed), while the collective is controlled with the left hand.

(image from Wikimedia, from Helicopter flight controls)
The pitch angle of the blades is modified with a swashplate. The swashplate can be raised as a whole (collectively, hence the name collective) to increase the pitch everywhere, or in a given direction resulting in different pitch angles during one turn (cyclically, hence the name cyclic).

(image from Wikimedia)

I am asking how the name was derived which it is not representing its function?

Interesting fact (at least for older aircraft and probably still true); the throttle was on the collective where the pilot's hand is applied and pulling the collective up results in a natural rotation of the throttle to increase power.

@AirCraft Lover The collective control changes the blades' pitch collectively (together), while the cyclic control changes the pitch of a blade in a consistent manner during different parts of the rotation cycle. Their names perfectly describe their function, in a very literal manner. It only seems odd if your grasp of the language doesn't sufficiently cover the varied usage/context of the words.

@AirCraftLover as aerobot said, the name comes from how the swashplate is moved, either collectively by the collective or cyclically by the cyclic. I clarified the answer.

As explained by John K above, "Collective" is short for "Collective Pitch Control." That's very reasonable.


text:
For civil or passenger airplane, is any moment that left and right elevator activated differently?

Source: Wikipedia
I want to know if any moment that the left and right elevator are activated (used/functioned) differently of a civil or passenger airplane. Here I am talking about civil airplane, not a fighter jet. I.e., one (side) elevator is pulled up/down while another elevator of another side remain "neutral" or neither pulled up nor pulled down. If any, when or in what condition?

Don't have the time to type this up, so will comment rather than answer (but somebody else is welcome to): https://flightinfo.com/threads/dc-9-split-elevator.69703/ and https://www.airliners.net/forum/viewtopic.php?t=74675  and https://www.jetphotos.com/photo/6567073

No, there is no situation where left and right elevators are intentionally deflected differently in any civil aircraft.  (I assume that the "ruddervators" of V-tailed airplanes don't count!)

Do any commercial planes have single sided trim tabs? Certainly some GA planes do.

@tedder42 Transport category aeroplanes typically use a THS (trimmable horizontal stabilizer), not trim tabs.

Yes, I am talking common airplane that their tail is like in the picture which they has vertical and horizontal stabilizer. V-tail or inverted V-tail, or other similar is not included.

@tedder42, I don't really understand you you mentioned. As my question, if any moment that left and right elevator activated differently, when or in what condition?

@aircraftlover I don't know what categories either be included under "common airplane" but thanks bianfable, didn't know for sure if large commercial/transport had anything single sided.

Some Boeing aircraft can have split controls iirc, where if enough force is applied the left seat controls the left elevator and vice versa

Just to add something to @quietflyer answer.
This is the schematics of the B747's hydraulic system:

For safety reasons it is quadruple-redundant, with each moving surface split into two parts each driven by one or two different systems. As visible, the following connection exist for the elevators:

left outboard elevator $\rightarrow$ 1
left inboard elevator $\rightarrow$ 1+2
right inboard elevator $\rightarrow$ 3+4
right outboard elevator $\rightarrow$ 4

So, in case of failure of systems 1 and 2 (or 3 and 4) an asymmetrical movement of the elevators could actually happen.

That is true in case of failure. But failure means, no more option rather than have to do the available option. What I am asking is in an operation which no failure.

@AirCraftLover: "What I am asking is in an operation which no failure". Sorry it was not clear from you question.


text:
What are these SR-71 "Ports" for?
In this video at the 2:40 minute mark there is a relatively clear image of the rear of a Blackbird.  This is a new view - at least for me. Are those "ports" and, if so, what are they venting?  IF not, what are they?
Here is a snapshot at roughly that time:

please update the link.

According to the SR-71 handbook section 6-11, these are fuel dump vents (outer) and fuel tank pressure relief vent (center).
Since this is copyrighted material, I will not include a screenshot of the page, please follow the link above to view the page.
In some models these vents were relocated, because a camera system air conditioning appendage was added to the tail of the plane

In action


text:
Are narrow propellers more efficient than wider ones?
I came across this company E-Props that builds propellers and it seems like all their propellers are narrower, at least narrower than traditional ones I'm used to see, and I see on their picture gallery many aircraft using them, almost like a trend. Are these props more efficient, cost effective, or is just a trend or something?
What's the deal with it?

(source)

Same as the wings, aspect ratio.

Propeller chord is determined by the power which needs to be absorbed by the prop. As with wings, propeller blades perform best in a small band of lift coefficient values: Too high, and drag will become excessive, too low, and you need to spin more surface area through a viscous medium (air) than necessary.
One further consideration is Mach effects: For that reason, the lift coefficient values of the Junkers VS-9 propeller were kept low by widening the chord of the propeller blades. It worked indeed better than conventional propellers at high speed, but that line of development was quickly eclipsed by jet engines.

FW-190 / Ta-152 with Jumo 213 and VS-9 propeller.

I think here there's both a clever use of the structural characteristics given by carbon fiber and some marketing at work.
We can try to answer this question using one of their documents (PDF) to better understand their choices.

The E-PROPS propellers have a thin chord (chord = width of the blade). A thin chord generates less drag than a wide chord and leads to a better efficiency of the propeller, a better thrust, makes less noise and reduces fuel consumption

That's the marketing department speaking: lower chord means lower Reynolds number which, contrary to this claim, is actually connected with slightly higher drag and lower $C_{l_{max}}$.

With E-Props designs and profiles, for the same diameter, more blades = more efficiency. A 3-blade has a best efficiency (= a best thrust) than a 2-blade.

That can be true. Normally it's preferred to have a number of blades as low as possible: this gives a lower cost and weight overall. Anyway if the number of blades is incremented then they get a higher aspect ratio and therefore lower induced drag which (more than?) compensates for the higher drag due to the lower Reynolds number. More blades also give lower vibrations and a "more  uniform" wake. Obviously a slender blade deforms more than a stubby one but this is where the clever use of carbon fibre I was mentioning comes into play.

The increase of the diameter is better for the efficiency, because of the improvement of the pusher efficiency. More static thrust is obtained with a propeller with a diameter of 180 cm than with a propeller with a diameter of 155 cm. With the same number of blades, the thrust gap depends on the diameters and on the engine + reducer.

Obviously a bigger blade delivers more thrust! Anyway that must be combined with a slower rotating speed otherwise the tip can reach transonic speeds with a big increase in drag and noise.

Are these props more efficient, cost effective, or is just a trend or something?

As seen, blade design is a compromise among contrasting requirements and it can be that more than one "shape" is able to deliver good aerodynamic characteristics.
It would be nice to compare their data with the ones of the propellers they replace in order to give a more solid answer.

Excellent!  I may have an historical perspective regarding thinner blades and thrust, and why fat bladed propellers are used.  The observed marketing and performance aspect of these new composite blades was also interesting. Superbly discussed!

@ThomasPerry: thanks

@sophit Interesting the first point you bring from their PDF document I also thought it was that way. Like in wings (like in a glider) it is supposedly more efficient. In the end I think it is as has been said in other things in aerodynamics: you gain from one area and lose from another area. But yeah as you put it in your last sentence it would've been nice some data to compare to.


text:
Are Designated Pilot Examiners (DPE)s incentivized to fail people on checkrides so they can collect extra money on re-tests?
I'm almost ready for my private pilot checkride, and it seems to me there is a perverse incentive for DPEs in passing or failing people.
If a DPE makes additional money on re-checks for students who fail the checkride, then it seems to me that DPEs have have a strong financial incentive to fail people the first time so that they can collect additional fees on the re-test. In fact, it seems that there are no rules in place to stop a DPE from making a student do the checkride 4, 5, or 6 times and collecting additional money from the student every time.
The checkride fee is exorbitant ($900 here in Southern California), but I'm even more concerned that the DPE would be hoping to fail me so they could collect extra money from me on a re-check. It actually makes my blood boil just thinking about it.
I'm not saying that DPEs are bad people, but the incentive structure certainly seems to make it easy for them to exploit eager students, and if economics has taught us anything, it has taught us that people respond to incentives.

Flight instructors get punished for failed DPE/checkrides, by extension the DPE's want to work with FI's to get more business, so failing a checkride too many times hurts the FI and hurts the DPE's references. 3 failed checkrides often results in a "709" ride for the CFI, and a bench until they can pass it.

Welcome to Av.SE.  Any DPE that gets that reputation won't be giving many checkrides at all, before very long!  As Ron Beyer describes, the CFI's would have a strong incentive to warn students away from the DPE who's likely to fail you for the sorts of reasons that you describe.

@ymb1, don't you like my answer?! ;)

What does DPE stand for?

I think you are getting worked up about something that isn't a problem.  DPEs are incentivized to develop a professional reputation that upholds appropriate standards, while passing those who meet the standard.  Someone who is motivated by greed to fail students as you suggest would quickly get a bad reputation and people would simply stop scheduling check rides with him/her, so the plan would rapidly backfire.
Think about it, I could easily make the opposite case that I am concerned about safety because a DPE motivated by the desire to get a reputation of passing people the first time to increase his/her business could be tempted to compromise on the standards.  It should all balance out in the end.

Giving weight to your second paragraph, in 1994/1995 DOT determined that DPEs were passing 90% of applicants on unobserved checkrides and 70% of applicants on observed rides. Page 10 of the document, PDF page 15.  When you are on your checkride, everyone involved wants you to pass.

@SteveV. On the other hand, DPEs whose pass rate is higher than 90% are supposed to be "flagged" (your PDF page 2). So I guess someone could be the unlucky guy where the DPE "needs to fail somebody" to have a quiet life!

@alephzero - If someone is in the bottom 10% of applicants that a DPE has seen lately I struggle to call that "unlucky", but I take your point.  :)


text:
How does WiFi work on an aircraft?
I've noticed that when a WiFi system is set up on an aircraft, a small bulbous structure is added. What does it contain and how does this WiFi system work?

The small bulb houses the antenna that provides the satellite communications for the internet link.
Inside the aircraft several wireless access points provide a WIFI signal to the passenger's equipment. The wireless access points are connected to a central modem which in turn is connected to the transceiver unit. The transceiver uses the rooftop antenna to communicate to a geostationary satellite.

source: dailywireless

source: Flightglobal

The antenna is a small dish or phased array that is aimed at the communication satellite using servo motors and/or electronic beam steering. The antenna control system receives information about the position and attitude of the aircraft to calculate the relative position to the geostationary satellites that provides the internet communications signal.
There are also systems available on the market that use a ground based network to communicate with the internet. These systems cannot provide global coverage since the aircraft needs to be in line of radio sight of a ground based antenna.

Wow, phased array... It's only thanks to your post that I can fully appreciate the simplest thing like a normal wifi conncetion I'm used to get all over the place.

The wifi connection (link between your device and the wifi router in the airplane) is pretty conventional, in the exact same manner as the wifi connection in your home or a cafe. The pictured device and antenna are for the internet connection between the airplane and the rest of the world - replacing the cable or fiber optic connection that you or the cafe might have to your internet service provider.

Possibly Pavel is confused about the difference between Wi-Fi and the Internet?

@immibis: I just didn't make myself crystal clear, that's all. I used to work in wireless network business (where I got the feeling of omnipresent wireless connection to the Internet) as well as non-destructive material testing, where I got to appreciate the technical and computational complexity of phased array. I have yet to get to building and launching a communication satellite, though.

While I see the image from Lufthansa above. They turn off the WiFi called "Fly-Net" above mainland China, beause "free as in free speech" ist not available above China. However, I'm glad that it is not allowed to make calls during flight and being not available is a pleasure.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
How can I easily keep track of my landing count during pattern work?
PPL Student pilot, ~20 hrs
Hi,
whilst doing some pattern work I frequently find myself unable to keep accurate track of the number of landings. There's an AFIS at my home airport who keeps track (because they charge fees) but there are a few "flatrate" (you pay for 5 landings, but it's flat-rate after 5) air fields or some free gras strips where nobody keeps count.
The flat-rate one is particularly hard, the pattern altitude is just 650 ft and it's very tight, so there's barely any chance even on the downwind to scribble a note on paper or so.
I've tried using a "lap timer" function on my watch, scribbling lines on a tally sheet etc, but am prone to forget to add a line when things get busy. My multi-tasking capability hasn't improved to the point where I can do too many things at once.
An extrapolation of flight time and time per pattern isn't always giving me the correct answer either.
Would the Pros have any tips on what might be a useful way to keep an accurate count of the landings? How are you doing that?
Update 14/07/2020
Based on the @Bianfable's tip, I've installed "Altimeter Plus" on Android, and had that active. I thought I'd share the results with you:

My problem is solved. I've flown 11 patterns, which are clearly visible (marked yellow). I've done two engine failure after takeoff trainings, marked blue. The red marker must have been a sensor error; I don't remember crashing between the first and second landing. The green markers are forced landings w/o power, aborted at about 350 feet each.
The bad thing about it: Although it was gusty and there were strong winds, I can now see that my altitude control could be improved in the pattern. I don't ever remember being more than 50 feet off, but the data suggests otherwise.
Once again, fabulous tips all, but this was the winner. Phone in my pocket keeps count, and provides reprimands to beat oneself up about after landing. Great! Even provides pretty accurate flight time, next time I'll try and activate it on top of the hour for easier calculation of what time second "x" actually is.
Next time I'll also have phyphox running and will measure the acceleration on landing. The next thing to improve...

Great to see it works well :) By the way, I wouldn't beat myself up if the altitude shown here is incorrect. I am not sure how well these sensors are calibrated and I wouldn't trust the absolute values shown (the altimeter in your aircraft should be used for that). But pressure differences are clearly visible :)

I'm not too unhappy - my FI is pretty strict (I'm actually happy about it!), his saying is "I'm not happy, until you're not happy" - he would have said something if the altimeter had ever moved 50 feet out of the assigned altitude. In reality that is obviously the only instrument I care about - but it's good to see there are additional backups next to the Alt Static, Transponder or GPS.

Nice solution. I'd probably verify the sensor is accurate before relying on this. Just get up to an altitude, and verify the phone matches pretty closely if not exact. Might explain your "crash" or general jitter in the reported altitudes.

Another alternative is to pick up a "knitting row counter", they come in rings you wear on your finger and you just push to increment them: Row Counter Ring.

Regarding your update, I would just point out that the altimeter in your airplane is probably more reliable for relative small changes than the altitude readout on a smartphone app. It's possible that your altitude control needs some work, but it's also possible that there's just noise in the data from your phone (e.g. from not getting an actual GPS fix each time and the phone just trying to extrapolate from accelerometers.)

@reirab I've looked again today, and never deviated more than 10 feet - the output is identical. So it's probably noise. Also it's in my pocket, ie on a kind-of alternate static. Of course the only thing I rely on is my altimeter (although I've just learned to live without it - got pitch and power setting accurate to 2 knots now. So proud! ;-)

GPS are particularly bad at measuring altitude, partly because of the geometry of the fix, and partially because they are mostly used to locate on a map, and vertical accuracy is usually not that important. You can improve it a bit by placing it next to a window.

cellphone altimeter is GPS with a very cheap anntenna, so it's not very accurate at all.

Just squawk 7495 and bump from there ;D

For after the fact counts, I've used websites like flightradar24 or flightaware before. This requires good ADSB coverage where you're practicing and an airplane with ADSB though.

The other answers have provided some easy ways to increment your count without too much distraction, but if you are really "prone to forget [...] when things get busy" as you say, this might not be good enough. I would therefore recommend a solution which does not require any action on your side.
Most smartphones today have a pressure sensor. There are apps that can record the pressure data over time (e.g. this one). All you have to do is start the recording before you go flying and then later look at the pressure vs. time plot. In an un-pressurized aircraft it will be easy to see your landings (these sensors are typically accurate enough to tell the difference between your feet and your head).
Alternatively, you could record your GPS position over time (e.g. this app) and look at your flights that way. Note that both of these options would work even with the phone in flight mode.

Fabulous, never thought of that. I'll try both approaches later today and will report back.
With the app you mentioned, the min interval appears to be 5 min for collection, I'll see if that screws up the result (say it takes a data point on base, the next one will most likely be base again...

@ExternalUse Sorry, I didn't check the recording intervals or max. recording times for these apps. One may have to look for apps better suited for this application. Personally, I am using phyphox for recording sensor data (disclaimer: I work for the university which developed this app, but I am not associated with its development). You'll have to see what works best for you...

Just had a look around and found "Altimeter Plus" which appears to record (on demand) in 1s Intervals. It's free w/o Ads. Phyphox looks really interesting, too - well worth a second look from what I've glanced at. Thanks for all suggestions!

I was going to suggest a GPS tracker, too. I use my phone for running, an I can follow my track to keep track of laps around a 400m track, so I'd imagine that you could do the same for keep track of laps in the pattern. Of course, that presumes you're making a landing approach on each lap...

@FreeMan GPS can also record altitude (although with less accuracy), so that shouldn't be a problem, unless you execute a go around at very low altitude. My concern is more that the signal strength inside the aircraft might be insufficient for the small antenna in the phone and you wouldn't notice problems until after landing. That's why I think the pressure sensor is more reliable.

If only my phone had a barometer, @Bianfable, but I fully get your point. :(

I'm accepting this as the answer, because in a way that's what I ended up doing.

The trick my CFI taught me is to use your Course Deviation Indicator or ADF to keep track of landings. After your first landing, bug a course of 010. After your second landing, bug 020. You can reach over and adjust the knob after every landing without having to juggle a pen and a notebook. It's still a manual step, though.
You could also use a product like Foreflight or CloudAhoy or even a service like ADSBExchange to count the number of approaches you made after the fact.

I do like that, might even be able to get this worked into my downwind checks.Thanks!

This sounded great, but today in p...poor vis and low ceilings we had everything (ILS, NDB) tuned in just in case, so it wouldn't have worked. I'll stick with Bianfable's method now, it's really nice.

Get a Tally Counter, and push the button once per landing. No batteries, nothing to fail, easy to use. Not much more you could ask for.

https://tallycounterstore.com/finger-tally-counter-quantity-discounts/
There are even options for mounted ones.

https://tallycounterstore.com/mounted-tally-counter/

I think I found my solution - about to update my question with the test results! Thanks anyway!

Controllers use a counter very like this (actually more similar to this version) to keep counts of operations in the pattern as well! Very old-school but it works, as long as you remember to use it.

(Disclaimer: I'm not a pro at all, I don't even have any license yet)
If you do indeed have a smartphone with you, you might consider just letting a voice recording run for the duration of your pattern work and call out your landings. When you're back on the ground, you can just listen through the recording and count the landings.
This might also have another interesting use, as you could actually comment on your maneuvers, i.e. if you're happy or unhappy with something, so you could analyse it later.
Afaik, Flight Chops (the aviation youtuber) initially started recording his flights on camera in order to be able to analyse them later, so that might be a way as well.
(Also, welcome to aviation.stackexchange )

Not on a full CVR, but it would at least get your half of the conversation. "Come on... lower... I need to be a bit lower! No, flaps sooner!"

Of course, I haven't thought about the decent amount of noise these small airplanes make :D Maybe there's a way to connect your phone to the com system so you can record everything?

Else, you just might have to scream at your phone a bit :D

Surely just putting your phone in a holder so it's pointing out the window, with a timed photo app taking a low res pic every minute, then - defeats the noise issue and should be visually obvious if youre on land!

Pace count beads, which are just some beads on a rope that doesn't let them readily move, would work well if you want to keep track while in the air.

Nice one. These are also sometimes called Ranger beads. I thought about this too. Glad you posted it! Welcome to the site.

Fun idea - might be mistaken for praying though. Might take a student longer to solo if the FI always thinks he's praying to make it ;-)

Almost every calculator can be converted into counter just by typing something like 1 + = (and then every time you press = the value is incremented).
This can be used if you need aircraft instruments for the training itself instead.

Thanks, that's a good idea but impractical I fear. Keeping it on my lap won't work, and when putting it away it's likely that buttons would be pressed randomly in a side pocket etc. But thanks for the reply!

I use my ADF. Set the frequency to 1000 when I start, bump it by one for each landing.
(Might as well use it for SOMETHING!)

I asked my CFI this after a day where we did over a dozen landings. He showed me his kneeboard notebook - there was a neat little row of tally marks next to the METAR info for each field we'd landed at.
The trick he used was that he was marking takeoffs, because ultimately what takes off must land (note; this won't work for spaceplanes). During the climb you're really just holding it steady and listening for calls; I find in a c172 that's a good time to grab the pen and make a mark on the kneeboard.

Hmmmmm, dunno. During the climb to circuit height, I usually have my left on the yoke and the right on the throttle. If anything goes wrong I don't want to find myself fumbling around with a pen. The only few seconds where I relax is on the downwind usually. A simple gust or windshear might throw you into dangerous speed territory on climb, I don't want to have my eyes inside the plane or my concentration diluted too much then. Doesn't work for me.

Ultimately, all these solutions (beads, clicker, paper, HDG bug) require you to take a hand and touch something inside the plane; you'll just have to work out when you can do it, and be sure that you'll remember to do it on every departure or landing - not just pattern work. It's also worth tying or clipping your kneeboard pen so you don't fight with it when you need it (otherwise why have it?)


text:
Cessna 182Q (parachute operation) - climb leaning with CHT
for a 182Q the POH specifies for maximum climb to use 2400 RPM and full power with given speeds (78 KIAS for Sea Level, reducing to 72 at FL100). It specifies that the mixture may be leaned at 5000ft or above.
In order to become the best possible parachute ops pilot I can be, I'd like to improve my best rate of climb. We've got CHT monitoring but I can't find good suggestions on how to lean for best power whilst keeping the mixture agreeable for the engine at max power using the cylinder head temps.
If somebody could point me to a reputable source I could use to learn more I'd be delighted.
Alternatively; what methods do you employ to improve the climb? Every minute is valuable for dense parachute ops.

Sorry, I'll reword it to Parachute jumping.

Leaning won’t change your power just your fuel consumption. Air is the limiting factor- you just need to make sure you have enough fuel to ensure all the air is used.

Don't you also lose a bit of power when the mixture gets too rich? In a C172 we start leaning at 3000 in a climb, and you usually see the RPM increase a tad. There we lean on the EGT until it just "comes back alive".

Yeah, if you’re way off then the extra fuel will cool the cylinders significantly reducing the pressure therein.

Not sure if risking overheating an engine is worth saving 5 minutes in a climb, but if economics favor it, perhaps a dedicated turbocharged engine with adequate cooling (or even a turboprop) might be better at quickly bringing a load of parachutists up fast and safe.  More thrust is needed to climb faster.

@RobertDiGiovanni - Or even just getting a “climb” prop instead of the  general-purpose stock one.

It's a 182, so it's a constant speed prop.

@JohnK -  Doh!  You’re right!

Don't bother will all that.  Without a proper 6 channel Exhaust Gas Temperature gauge, and fuel injection, you can't hope to do any of that sort of anal-retentive leaning to the nth degree kind of stuff.  The O-470-U is carbureted, so you can't get even mixtures in all cylinders in the first place and without an EGT, leaning by ear and manifold pressure is all you have.
Leave it rich to 5000 ft, then lean to onset of roughness + a bit of rich and just leave it. Watch the CHTs and if they climb out of the green, either speed up or enrich some more (assuming cowl flaps are fully open).  You could futz around with the leaning to get to peak power, based on manifold pressure, but because it's declining as you climb you'd have to level off to do that, so it's not worth the trouble, although if you are listening carefully you might be able sense the best power sweet spot by playing with the mixture during the climb.
Focus more on being kind to the engine, which makes the owner happy, and planning your route during the climb to get to the level-off altitude, aligned on the proper ground track toward the Spot, with a minimum of screwing around, and that will make owner and the jumpers happy.  You will save way more fuel and time by arriving at the Spot as efficiently as possible, by anticipating where you need to fly to, than by any leaning protocol.

Thanks, that's very useful information and a well written reply.


text:
How to avoid getting trapped on top VFR?
This question addresses whether it is legal to fly VFR over-the-top.
One of the comments mentioned the difference between safety and legality, i.e. doing so may not be safe even if it is legal (in some places, for some pilots). The most obvious concern would be whether a VFR-only pilot could find a hole in the clouds to descend for landing. (There may be others.)
How exactly does one mitigate this risk to an acceptable level? Or is it generally accepted that, even though regulations don't say so, that it should only be done by pilots with an instrument rating?

By regulation you just have to be sure that the conditions at destination allow you to maintain VFR clearance from cloud for your descent.  Pretty much all you have to go on is the TAF for the area of your destination.  If there isn't a TAF for an airport within say 20 or 30 miles from destination that would be a problem for me.
Assuming a TAF is available, you technically could go if the forecast was for broken cloud below you, hoping for a large enough hole to get down (basically a hole at least 4000 feet across, with you in the middle of it).  But that's taking a bit of a risk.
It would be imprudent to go with anything more than scattered cloud in the TAF at any level below you at the time of your planned arrival.  And even scattered cloud in late afternoon is pushing it.  On top of that you are continuously monitoring the METAR at destination for detrimental changes, and you also have a planned alternate that has better forecast conditions than your destination.
One of the more important factors to keep in mind on a trip like that is the temperature/dew point spread at destination (which will determine the cloud base if there is enough humidity), and the time of day.  When I was bush flying in Northern Ontario many many years ago, with many hours spent scud running under low cloud, the dew point spread was the most important bit of weather information and a tighter spread was more acceptable in the morning than in the afternoon.
A morning trip, with a decent temp/dew point spread that makes unexpected cloud formation below your level unlikely with temperatures naturally destined to increase until early afternoon, is lot safer than an afternoon trip where the spread will be decreasing and more-than-forecast cloud formation at a level below you is more likely.
Personally, I would never do VFROTT because I'd be biting my nails the whole time worrying about the engine quitting (I've had a mechanical engine failure) and being forced to descend through a cloud layer and then trying to find a landing area underneath it, if there was a decent ceiling.
And there's the rub; you not only have to come up with good weather margins, you have to have iron clad confidence in your engine if you're doing it in a single (which lots of single-engine IFR pilots do - me not so much).

I've only done it with one CFI, who obviously had an IR. We agreed it was better to be higher and thus in gliding distance of some airport (albeit through clouds) for the entire trip. I suggested the same to another and he insisted on staying below the layer until I had my own IR, and following highways in case of emergency.